There are now available on the market alarm systems in which transmitter units respond to emergencies of various kinds to generate radio frequency transmissions communicated over wireless links to controllers adapted to provide alerts of such emergencies either by actuating local alarm devices such as sirens, or by sending signals indicative of the occurrence of such emergencies over a wire link to a central office.
One such alarm system is the Emergency Call System ("ECS") made and sold by the American Telephone and Telegraph Company. That system employs transmitter units adapted to be connected to sensors for detecting the happening of various emergency events such as a breaking of glass or a forced door entry (either indicating a forcible intrusion) the presence of smoke or the presence of some other potentially disastrous environmental condition. The transmitter unit comprises a printed wiring board, various electrical components mounted by the board for producing a radio frequency signal in response to detection by such a sensor of the occurrence of such an event, and a small antenna mounted on the board to transmit that signal by a wireless link through space to the controller.
Such an "emergency" signal takes the form of frequency modulation on a 40 MHz carrier, and the antenna for transmitting such signal takes the form of a short piece of wire rod having multiple "L" bends therein to provide the antenna in its middle section with two horizontal arms at right angles to each other and, at its extremities, with two additional vertical arms at right angles to such middle section and fastened at their free ends to the printed wiring board to mounted the antenna's middle section spaced away from the board in fixed parallel relation therewith.
At the relatively high frequency (40 MHz) of the carrier for the emergency signal, any substantial change in the positioning of the antenna from its predetermined desired positioning relative to the board can result in detuning of the antenna and consequent failure or degradation of the wireless link between the transmitter unit and the controller. Such mispositioning or deforming of the antenna can, however, easily occur during board-antenna assembly or later by the antenna being carelessly struck, roughly handled, or otherwise inadvertently misaligned or deformed.